Rigid coaxial transmission line systems in broadcast are typically very long. It is because of the length of the transmission lines that interconnections between segments are needed. The flange connection is constructed using a pressure fitted connector and supporting insulator. Supporting insulators positioned throughout the transmission line create small reflections because they disturb the electric field of the applied traveling wave. The flange connections typically create the largest reflections. Because so many flanges are needed to construct such a system, the sum total of all of the flange reflections can add to create an unsuitable operating condition.
As discussed in U.S. Pat. No. 5,455,548 issued to Grandchamp et al., the conventional method for overcoming such a condition has been to provide various lengths of transmission lines for different frequency segments. As best shown in FIG. 1, such prior art transmission line inner conductor segments 10 typically have a male end 12 and a female end 14, which allows two segments to be connected together to create longer transmission line lengths. The connection between two adjacent segments of transmission lines 10, 10a is shown in FIG. 2. Such prior art transmission line segments 10 typically include an anchor insulating support 16 positioned near the male end 12 of the transmission line segment 10. Additional mechanical supports 18, 18′ may be positioned along the axis of the transmission line segment 10. According to one preferred aspect of the invention, the mechanical supports 18, 18′ are positioned at equidistant intervals from each other and equidistant from the anchor insulating support 16. Depending on the length of the transmission line segment 10, more than two additional insulating supports may be provided. FIG. 3 and FIG. 4 depict simulated return loss and VSWR, respectively, at frequencies of 40 MHz to 860 MHz. for a conventional transmission line utilizing segments of 20 ft. to achieve a total length of 400 ft.
Thus, there is a need for a system and method for overcoming flange reflections in coaxial transmission lines where the transmission line is formed of multiple coaxial line segments of substantially the same length.